Vehicle air conditioning systems typically use a stacked plate type evaporator, often called a laminated evaporator in published patents. A common feature of such designs is integral flow tubes and headers made of aligned pairs of stamped plates. Each plate of each complete pair is generally rectangular, or at least longer than wide, and has an inner surface that faces the inner surface of the other plate, sealed together by brazing to create a thin, wide flow tube between the inner surfaces. The inner plate surfaces are often enhanced with bumps that braze to opposed bumps on the facing plate, strengthening the tube formed by the plate pair. Integrally stamped at the ends of the plates are open, protruding cups, typically one cup at each end, or two side by side cups at one end, which protrude away from the outer surface of the plates and are open to the inner surface of the plates. When the plate pairs (flow tubes) are stacked together to assemble the generally box shaped evaporator, the pairs of oppositely protruding cups align to create header pipes, either one pipe on each side of the heat exchanger (straight flow) or two adjacent pipes on one side (so called U flow). The two endmost plate pairs are generally are not complete pairs, that is, do not contain two identical stamped plates. Instead, the end plate of the first and last plate pairs is often simply flat, or at least has its cups closed off. This is because the two end plates simply provide end closures and/or a mounting surface for the inlet and outlet. The stacked cups of the complete plate pairs also act to space out the plate pairs to provide space for corrugated air cooling fins.
A continuing problem in the art of stacked, plate type evaporators has been the need for a compact arrangement of the regfrigerant inlet and outlet lines. That is, the ideal configuration is to have the inlet line to the inlet header and the outlet line from the outlet header directly adjacent, on just one side and the same end of the evaporator, at the same corner of the box, in effect. This is compact and easy to connect or disconnect from the rest of the system. This ideal is especially difficult to achieve, however, with the straight flow design, in which the header pipes are on opposite sides of the evaporator, running along the top and bottom of the box. With such a design, as illustrated in FIG. 5 of U.S. Pat. No. 5,101,891, the simplest configuration is one in which a short inlet line or fitting is fixed to the header pipe on one end and one side of the evaporator, and the outlet line is a short fitting diagonally opposed thereto, at the other side and other end. A long cross over pipe running outside of the evaporator would be needed to make the two fittings adjacent, at the same end and side.
Another continuing problem with the type of evaporator just described has been the need to distribute the refrigerant flow evenly throughout the evaporator, overcoming the natural tendency of the refrigerant to flow in a path of least resistance diagonally across the core from inlet to outlet, while not completely filling the other two comers of the core. This has been solved by so called multi passing of the flow, providing one or more barriers or separators in the header pipes to force the flow into a back and forth pattern, evenly distributed throughout the whole evaporator. With stamped plates, the separators can be conveniently and inexpensively providing by simply not punching the central hole in those plate cups where a flow barrier is desired. This, in turn, can be easily achieved just by retracting the punch that would normally pierce the stamped cup. A different or special stamping die is not needed to manufacture the barrier plate. An example of such a multi passed design can be seen in U.S. Pat. No. 4,274,482.
One embodiment in the just mentioned 4,724,482 patent illustrates the difficulty in providing compact inlets and outlets with a straight low design. The best that is achieved is to place the inlet and outlet fitting on the same end, but not the same side, of the evaporator, as illustrated in FIG. 5. But to do so, an embedded inlet pipe must be inserted down into one header, the embedded end of which must be sealed to a cup deep within the core, which is difficult to control. An alternate, multi passed, straight flow stacked plate evaporator design shown in U.S. Pat. No. 4,712,612 does not use an embedded inlet pipe, but again relies on long, external pipes to bring the otherwise distant inlet and outlet fittings adjacent to one another.
The so called U flow plate design, a typical example of which can be seen in U.S. Pat. No. 5,062,477, has the header pipes or tanks on the same side (top or bottom) of the box, but the simplest flow pattern still results in the inlet and outlet being on opposite ends of the evaporator, as shown in FIG. 1 thereof. Providing more complex, multi passed flow patterns in a U flow evaporator, while still placing the inlet and outlet fittings directly adjacent to one another is more complicated. Several examples of such in a U flow evaporator can be seen in U.S. Pat. No. 5,024,269. There, a combination of embedded inlet/outlet pipes and several different stamped plate shapes are used within each embodiment to achieve the desired end result. Neither embedded pipes nor a multiplicity of stamped plate shapes is desirable from a cost and ease of assembly standpoint. The U flow design shown in U.S. Pat. No. 4,589,265 puts the inlet and outlet fitting adjacent and avoids using embedded inlet or outlet pipes by incorporating that function into the drawn cups of some of the plates. Basically, the entire core is divided in half by two different types of complete plate pairs, and a complex flow pattern is created within the core that runs first in a U pattern from the near to the far end, then side to side (bottom to top) in another U pattern, and finally back from the far end to the near end. Again, a complex, U type flow pattern and several different plate designs are used just to locate the inlet and outlet in the desired location. More generally, U flow designs per se are undesirable when the core itself is shallow and each plate pair is narrow. Dividing an already narrow plate pair with the central rib necessary to give the characteristic U flow pattern creates even narrower flow paths and too large a pressure drop.